Furnace pressure switch line/nipple question

Furnace pressure switch line/nipple question

I recently had my inducer/exhaust fan replaced and several times since have found the new inducer fan running but the unit wouldn't fire up. On investigating I find that there are three hoses to the pressure switch. One is marked "-" and is attached to the inducer fan housing. The second marked "+" and connected to the "ignition box" (right name?). The third connects indirectly to the pressure switch by a "T" to the same place on the "ignition box" as the "+" hose, and is then connected to the "gas regulator" (right name?).

The non-flame up only happens occasionally, and can be overcome by sucking on the hose attached to the negative nipple.

Important point: The hose to the pressure switch that connects to the nipple marked "+" has a small plastic plug in it, that fits up into the nipple but cannot enter the nipple because of a small flange on the plug. The hose will fit over this grey plastic plug. This plug has a slot shaped hole in the flange end and a long slit and rectangular opening on the long shaft of the plug itself. Air can move through this plug.

Finally, here is my question: Is this plug a functioning piece of the pressure switch? Or just a leftover piece from when it was packaged?

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it is an orifice and MUST be there for the switch to be accurate. check your intake and exhaust pipes for blockage as that usually causes pressure switch tripping problems. post the brand and model # of the furnace for more info.